Solid-phase synthesis of N,N′-unsymmetrically substituted ureas:: Application to the synthesis of carbaza peptides

The synthesis of Boc- or Fmoc-monoprotected propylenediamine derivatives is reported starting from N-protected alpha-amino acids. The introduction of these building blocks on solid support via the formation of a urea moiety leads to a new pseudopeptide family (C-alpha-CH2-CH2-N-alpha(R)-CO-NH-C-alpha). Two carbonylating reagents, i.e N,N'-carbonyldiimidazole and triphosgene, as well as different coupling procedures, have been tested to optimize the Boc and Fmoc solid-phase synthesis of a model peptide incorporating this isosteric replacement. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.